Fuel injection system for compression-ignition engines



Nov. 23, 1943. s. HHNQHCMFFE FUEL INJECTION SYSTEM FOR COMPRESSIONIGNITON ENGINES Filed Feb. 13, lllzl Patented Nov. 23, 1943 FUELINJECTION SYSTEM FR COMPRES SIGN-IGNITION ENGINES Sydney lHinchclie,Wylam-on-Tyne, England Application February 13, 1941, Serial No.378,832`

In Great Britain January 29, 1940 Y claims (o1. 12a-139) Y Thisinvention relates to fuel injection systems for compression ignitionengines.

In the conventional fuel injection 4sy'stems the' fuel oil in thesystemfrom the injection pump to the injection valve-is stationary up tothe point of opening of the injection valve. The result is that when theinjection valve does open there is a substantial drop in the Ipressureof the oil at the injection nozzle, so that provision has to be made forcompensating for this. Otherwise the reduced pressure will result inpoor atomisation and thereiore'delayed ignition, with the iur` therresult that additional oil is being forced into the combustion chamberwithout being ignited, 'so 'that when ignition'does occurthere is anexcessively rapid rise of cylinder pressure which 'produces excessivemaximum pressures and temperatures in the engine. This compensation has-been effected by increasing the pressure generated by the pump toimpart the necessary high acceleration `.to the stationary oil in'orderto build up andmaintain the pressure at the injection nozzle at thatnecessary for atomisation. However, as is well known, such pumppressures are of excessive magnitudey and require pumps of suchsuperlative precision that their `production can be undertaken only bymanufacturers possessing special facilities. l

`It is thefobject of the present invention to provide means whereby suchexcessive pump pressures may be obviated, while at the same time thenecessary injection 'pressure may be maintained under precise controland so the point of ignition more 'accurately determined, with theYfurther `result `that'engines may be run morey smoothly` with reducedmaximum-pressures and temperatures withthe still further result ofincreased power/weight ratio. Another object is simultaneously toprovide means whereby a substantially finer. degree of atomisation isattained than hitherto,fso that engines may be run eiectively on'a widerrange of fueloils than has been hitherto possible with conventional fuelinjection systems. A further object is to provide means which willnullify the eiect of the expansion and contraction of the fuel oil pipeowing to the high pressures which have to be generated by the pump. Y

`A number of proposals have been made which included the use of anaccumulator piston which was adapted to move under the increasing oilpressure on the pressure stroke of the fuel pump until a predeterminedoil pressure was attained, whereupon ther injection valveopened andinjection took place, the accumulator piston being free to continue itsmovement so that the'injection pressure-thus depending solely on thestatic pressure in the oil system-remained substantially constant. Suchproposals included the use `of an injection valve connected to theaccumulatcr piston through a lost motion arrangement, so that after apredetermined movement of the said piston the injection valvewasopenedand continued to open in accordance with the difierence betweenthe increasing oil pressure and the pressure drop due to the opening ofthe injec tion valve.

`'Ihe fuel'injecton system according to the invention comprises aninjection valve adapted to be maintained on its seating by the fuel oilpressure, a fuel pipe, a pressure accumulator comprisin g a cylinder anda piston in said cylinder, said piston being adapted to be subjected tothe pressure of the oil in the system, the area of said piston beinggreater thanithat of the injection valve subjected to the fuel oilpressure, means for ar-A resting the movement of said piston at aboutthe timewhencommencement of injection is due, and

lost motion means operatively interposed between said accumulator pistonand said injection valve for opening said injection valve after the`said piston has moved for a predetermined distance under the rising oilpressure, the arrangement being such that subsequent movement of thesaid piston before its arrest is only suflicient to lift the fuelinjection valve the requisite amount ior Aefficient fuel injection.

The invention will now be `described by way of example with reference tothe accompanying drawing. Y

`In the said drawing:

Fig. l is a diagrammatic longitudinal sectional view of a form of theinvention comprising a combined pressure accumulator and cylinder.

Fig.. 2 is a diagrammatic longitudinal section of an alternative form ofpump to be used instead of the pump shown in Fig. 1.

Referring more particularly to Fig. 1, I is an vaccumulator cylinder,and 2 the accumulator piston. Sis an enlarged cylinder communicating andin axial alignment with the cylinder I. The cylinder 3 houses acompression spring 4 whose lower end abuts against the piston 2. Theupper end of the cylinder 3 has a vent 3a to prevent the building up ofpressure.

The piston 2 is adaptedto abut against an adjustable abutment screw 5 tolimit its upwardV The lower end of the piston 2 projectsV travel.

into an enlarged cavity 6, and is T-slotted at 2a to receive the headedend 1a of the valve stem 1 hand is slightly less than the distancebetween the end of theV abutment screw and the upper end of the piston2, by an amount equal to the lift necessary for the valve 1b.

' The spring 8 is purely supplementary, and ensures the valve lb beingretained on its seating when the engine is stopped and there ls no oilprg-ESSUIE.

Oil is forced by the pump B through the pipe I0 into the cavity B belowthe piston 2, and the resulting oil pressure causes the piston 2 tomoveupwards; but it maintains the valve lb on its seating until, aftermoving-upwards for a certain distance, the shoulder 2b of the piston 2abuts against the under side of the head la, and so begins to liftthevalve 1b, lifting continuing until the movement of the piston 2 isarrested by the abutment screw 5.

Owing to the movement of the piston 2, the oil .is able to gain momentumthrough the pipe I0,

to that of the piston portion I2a is moved along the pipe I0 before thepiston 2 begins to lift the valve lb. Thus the oil in the pipe I0 isaccelerated before injection starts, and so has been allowed to gainmomentum.

It will be observed that the oil pressure except I when injection istaking place is forcingfthe injection valve 'Ib on to its seat, thustending to prevent leakage.l I

In the conventional arrangement there is a delay between thecommencement of pump delivery and the opening of the injection valve dueto the expansion of the pipes and other parts from a small pressure tothe high pressure necesceiving the oil. The said oil receiving means maycomprise, as shown, a spill v'alve II,' the oilpassing from the passageIU to the discharge port B of the pump B where the spill valve I I willhave been lifted, thus allowing the oil toescape to the suction chamberB2 of the pump B.

An injector as shown in Fig. 1 may be used,

if desired, with fuel pumps such as that Vshown in Fig. 2, that is tosay pumps which spill from the Vpump cylinders, and not from thedelivery pas- *sagev as is the case with the pump B of Fig. 1.

The delivery valve I2 of the pump C shown in Fig. 2 may have a portionof it arranged to act as a piston I2a as shown. With such an arrangementthe fuel pump now delivers oil to the accumulator cylinder until theaccumulator piston has reached its stop 5. mences and continues untilthe spill valve I3 opens. At this point the delivery valve I2 closes,but owing to its piston portion I 2a there is displaced along the pumpdelivery pipe by the piston 2 a volume of oil equalto the volume of thesaid piston portion, thus allowing the valve 'Ib to seat and the piston2 to maintain a pressure on the oil. l

The motion of the accumulator piston 2 is nally Yarrested by the valvehead 'Ia or by the oil trapped in the system when the delivery valvereaches its seat, according to the relative volumes displaced by theaccumulator piston 2 and the piston portion I2a of the delivery valveI2. By keeping the volume of the piston portion I2a less than themaximum displacement of the accumulator piston, the delivery valve I2seats before the accumulator piston reaches the valve head la, and thepressure is thusY maintained on the oil system between consecutiveperiods of injection. When the succeeding delivery of the pump begins, aAvolume of oil approximately equal Injection then com-Y sary to open theinjection valve. This causes variations ln the actual point of injectionand reduces the engine efficiency.

With the smaller -pressure increases required by the arrangementaccording to the invention this drawback is obviated and a more delicatecontrol of the fuel ignition point may be effected.

Again, owing to ytherfact that' the suitability of Diesel engine oilsdepends on the rapidity with which they ignite, and aslgnition is afunction of initial atomisation', vthe invention permits the use ofa'wider range offfuels than hitherto.

The advantages above set forth are more marked in contrast .with theconventional fuel injection Vsystems at high engine speeds. Theoperation ofthe system according to the invention is practicallyindependent` of the engine speedf and therefore isvof specialadvantagefor variable speed engines. 1

Another result of the system according to the invention effects the fuelnozzle. 'lhel size of nozzle orifcevi's chiefly a function of the fuelquantity, the duration of the injection and the mean pressure of thefuel. As the system according to tne'invention reduces the mean fuelpressure, the'siae of orifice can be increased. The nozzle istherefore'cheaper to make but also makes possible the use o f orificeshapes other than circular or annular-`-which are not necessarily thebest-for atornising'. This effect is progressive because by using a moreefficient atomismg shape the pressure can again be reduced and so on.

What I claim as my invention and desire to secure by Letters Patent ofthe United States is:

l. A fuel injection system comprising an injection valve adapted tobemaintained on its seating by the fuel oil pressure, a fuel pipe, apressure accumulator comprisingva cylinder VVVand a piston in saidcylinder, said piston being adapted to be subjected to the pressureofthe oil in the system, the area of said piston being greater than thatof the injection valve subjected to the fuel oil pressure, means forarresting. the movement of said piston at about the time whencommencement of injection is due, and lost motion means operativelyinterposed between saidaccumulator piston and said injection valve foropening said injection valve after said piston has moved for apredetermined distance under the oil pressure, the arrangement beingsuch that subsequent movement of the said piston vbefore its arrest isonly sufficient to lift the fuel injection valve the requisite amountfor efllclent fuel injection. v

2. A fuel injection system according to claim 1, a shoulder on theaccumulatorpiston, said shoulder beingV adapted to engage an abutment onthe assunse injection valve after the predetermined amount of movementoi' said piston has taken place.

3. A fuel injection system according to claim 1. wherein the accumulatorpiston has formed thereon a T-slot, an abutment screw adapted to abutagainst the inner end of the accumulator piston, a valve stem integralwith the injection valve, a, head on the end of said valve stem, saidhead engaging with the T-slot in the accumulator piston, a springadapted to press the inner wall of said T-s1ot against the outer face ofsaid head, while the lower face of said head is adapted to abut againstthe shoulder formed by said T-slot, the diierence between the lengths ofsaid head and the distance between the inner face of said lo slot andthe inner face of said shoulder, being pump.

slightly less than the distance between said abutment screw and thepiston when the injection valve is closed, by an amount equal to thelift necessary for the injection valve.

4. A fuel injection system according to claim 1, comprising means formaintaining the pressure during the period between consecutiveinjections in the fuel oil pipe line at a value approximating thatrequired for injection, said means comprising a fuel pump delivery valvehaving a piston portion thereon which allows its ownvoluxne of oil tomove along the fuel pipe before opening and closing of the said deliveryyalve, and a. spill valve betweensaid delivery valve and the fuel SYDNEYHINCHCLIFFE.

